The U.S.-Mexican border is the front line in the war against illegal drugs. That fight is increasingly technological, and the Border Patrol recently gave Popular Mechanics a front-row seat.

Somewhere east of El Paso, Texas, a metal pavilion straddles the eastbound side of the highway, flanked by a single-story building. Cameras scan approaching cars. By the time a vehicle stops, its license plate has already run through a computer database.

This is just one way U.S. Border Patrol agents are using tech to try to stem the flow of drugs and illegal immigration at the U.S.-Mexico border. Agents still rely on classic strategies, such as dogs, to sniff for hidden passengers or drugs but now their arsenal is growing.

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Surprise Checkpoints

Using a fiberoptic scope, agents can peer into fuel tanks and through air-conditioning vents. Sometimes they see a frightened person staring back. Other times they find a hidden stash of drugs. Agents have found people hiding in engine compartments, dashboards, and once even inside a jet-ski hull. Drugs have turned up in wiper fluid reservoirs and in diaper bags.

After agents search a car, a white van pulls up alongside. The Z Backscatter Van looks unassuming, but this $750,000 piece of equipment carries a mobile Z backscatter X-ray machine mounted on a Ford F550 chassis. "We have to clear the vehicle of any smuggled humans first," one operator told Popular Mechanics—although the X-rays are not harmful to humans during one exposure, the Border Patrol does not scan people. Organic materials such as hidden drugs, even if hidden beneath false floors or in barrels, show up as bright shapes on a screen in the cabin.

Inside the checkpoint itself, a digital fingerprinting system provides instant response from federal databases. "We need to make that connection, get that information, as quickly as possible for officers' safety," Border Patrol agent George Gomez says. "But we also have to take into consideration the traveling motorist."

Because these checkpoints are located along highways about 30 miles inside the U.S. border and are not well known on the other side, they come as a surprise to many smugglers and illegal immigrants, who may think the challenges of border security are behind them. Agents say this unexpectedness is part of what makes the checkpoints effective. Still, they are a secondary line of defense. The primary line is along the 1954-mile border itself.

Looking Out

One high-tech surveillance tool sits alongside a desert highway outside El Paso, roughly parallel to the end of the pedestrian border fence. The position commands a view of the Rio Grande valley, especially through the optical/infrared camera and ground-scanning radar mounted in the Ford's flatbed. This year the Department of Homeland Security spent $5 million on these units. "That machine can cover up to about a 15-mile radius," Gomez said. "Now you have three agents out here, where before you had to have 15."

Inside the Z Backscatter Van, a monitor displays a map of the area, flecked with green dots where the radar detects movement. An operator tells PM that based on the location and size of the dots, he can usually tell whether movement is caused by a vehicle or foot traffic. The second monitor's real-time feed from the camera can pan and zoom as needed. If the operator spots potential trouble, he can radio other agents to investigate and then either transmit GPS coordinates to responding agents or guide them in by radio.

In even more remote areas Border Patrol agents still rely on tracking, or sign-cutting techniques, which the region's natives have practiced for centuries. Agents look for signs of human passage such as tire tracks, footprints, and even the faint marks in the sand where traffickers have tried to wipe away their tracks. The most skilled agents can glean the size of a group, its speed and direction, and whether it includes children, from these subtle signs in the desert. While using these centuries-old tracking methods, some of the agents carry Recon III thermal imaging binoculars, which allow them to see up to 7 miles across the desert, or they patrol in pickup trucks carrying FLIR units.

Near downtown El Paso, Border Patrol agents in green-and-white SUVs wait a few hundred yards apart along the 18-foot fence separating the city from the Rio Grande. Although the urban border is more secure than it was a decade ago, attempted crossings remain common even here—and smugglers have their own surveillance tools. An agent points to a house in Ciudad Juarez, Mexico, with tinted windows. "The cartels station people in houses like that with binoculars and cellphones to do countersurveillance on us," he says.

2000 Miles

"Here in El Paso," Gomez says, "we have a working control of the sector. A lot of the traffic now is being pushed west of us, to Arizona, and especially to South Texas."

In fact, Border Patrol stations in South Texas are so overrun with traffic from Central and South America that their colleagues in El Paso established two satellite processing centers. Agents use webcams to question and process illegal immigrants remotely—more than 100 a day.